The present invention refers to a method of and arrangement for rehabilitating a ballast bed of a track by installing a protective layer between a subgrade and a layer of ballast.
In general, rehabilitation of a ballast bed includes a continuous removal of old ballast to expose the subgrade, discharging a gravel-sand layer over the exposed subgrade and forming a protective layer for the subgrade by compacting the sand layer.
U.S. Pat. No. 4,479,439 discloses a mobile arrangement for improving a track bed by continuously laying a protective sand layer between the subgrade and the ballast of the track bed during continuous travel of a work vehicle in operating direction. A vertically adjustable excavating chain and conveyer belts for receiving and transporting old ballast are arranged between two undercarriages of the work vehicle which are provided for mobility of the work vehicle on the track. Trailing the excavating chain in operating direction is the discharge end of a conveyer belt assembly consisting of several conveyer belts arranged in succession in operating direction for transport of sand which forms the protective layer for the subgrade. A further conveyer belt assembly for introduction of new ballast is provided with its discharge end behind the discharge end for laying the sand. The work vehicle is further provided with a track lifting unit for raising the track essentially centrally between the on-track undercarriages and to allow a continuous removal of dirty or fouled ballast. At the same time, sand is conveyed to the construction site, and the sand is continuously distributed over the width of the track bed and drops through the crib onto the exposed subgrade. After compacting the sand over the subgrade, new ballast is continuously discharged and planed over the protective sand layer.
U.S. Pat. No. 4,357,874 describes a further mobile arrangement for improving a track bed with two independent and self-propelled work vehicles. Both work vehicles are provided with an overhanging machine frame and have on one end a vertically adjustable hoist which is supported on both sides upon an undercarriage. At the construction site, an assembled track section is lifted by the hoist off the track bed and displaced towards a remote end of the machine frame of the first vehicle. Subsequently, fouled ballast is removed by the excavating means which is mounted on the second work vehicle. The first work vehicle is then moved over the trackless renewal section for discharging and compacting sand and new ballast over the trackless renewal section. Thereafter, the detached assembled track section is lowered by the hoist onto the rehabilitated renewal section. The mobile arrangement and method according to U.S. Pat. No. 4,357,874 is suitable for rehabilitating short track sections.
The publication entitled "Verfahren zur Verbesserung des Planums auf vorhandenen Strecken", UIC-Codex 722E, Internationaler Eisenbahnverband, Jan. 1, 1990, page 11, describes another method of improving the subgrade of a track by initially completely removing the fouled ballast by means of a bed cleaning machine. Removed material is partially laterally deposited or loaded onto suitable freight cars. Next, exposed subgrade is leveled, possibly with a geotextile installed under the track between the ballast and the subgrade, and the track is placed over the subgrade. Thereafter, a gravel-sand layer is discharged from a dump car and distributed to the required level with a ballast planing machine. Subsequently, a tamping and lining machine lifts the track panel off the track and compacts the gravel-sand layer under the ties with enlarged tamping picks. Finally, ballast is discharged from the dump car, the track is lifted, the ballast is tamped and the track is correctly aligned.
German patent specification DE 42 37 712 A 1 describes yet another mobile arrangement for rehabilitating the track bed, including two separate work vehicles, with one work vehicle supporting an excavating means for removing old ballast and the other work vehicle supporting a track lifting unit as well as a planing and compacting unit.